In patients in need of cardiac resynchronization therapy (CRT) the left ventricle electrodes are almost exclusively placed epicardially, either directly on the epicardial surface or through a coronary vein. This results in a pacing activation sequence very different from normal physiology, where the myocardium normally is activated from the endocardial surface to the epicardium resulting in specific improvement of cardiac efficiency and reduction of shear forces within the ventricular wall. The natural activation sequence is generally better than “total synchronization” in terms of achieving physiologically suitable heart contraction and should be mimicked as close as possible.
Somewhat diverging views exist about how the myocardium is organized. The cardiac surgeon Gerald D Buckberg at UCLA bases his understanding of cardiac action on the Spanish anatomist Francis Torrent-Guasp who claims that the left ventricular myocardium can be dissected and functionally described as consisting of a myocardial band divided in three “sub-bands”: the basal loop, the descending loop and the ascending loop. These loops are activated in sequence resulting in an initial basal contraction rotating the basal heart clock-wise as seen from apex and reducing the diameter of the mitral annulus, an early systolic apical clockwise torsion movement followed by a counterclockwise torsion during the main part of systolic emptying. Of specific interest is the initiation of diastole, where Buckberg and others think that an active untwisting movement (caused by muscular contraction in epicardial layers of the “ascending loop”) adds to the elastic recoil reinforcing left ventricular filling.
Other researchers claim that the myocardial band does not exist as an anatomical entity and that the myocardium is better described as a continuous syncytium of muscular cells with varying orientations depending on the distance from the endocardium.
Although different views exist it is still accepted that an initial basal contraction decreases mitral annular diameter early in systole. The majority of the left ventricular mass is activated from the endocardium to the epicardium resulting in an initial clock-wise rotation and somewhat later a dominating systolic counter clock-wise rotation associated with left ventricular shortening. An “untwist” is seen during diastole accompanied by lengthening and widening of the left ventricle.
There is, thus, a need for a technique that can be used to provide CRT that is physiologically adapted to subjects in need thereof.
U.S. Pat. No. 7,840,266 discloses a lead assembly adapted for placement in a coronary sinus and having a left ventricular electrode adapted to deliver CRT to reduce ventricular wall stress. A fat pad electrode is also provided on the lead assembly to be positioned proximal to a parasympathetic ganglia located in a fat pad bounded by the inferior vena cava and the left atrium. The fat pad electrode is adapted to stimulate the parasympathetic ganglia to reduce ventricular wall stress.
US 2004/0015193 relates to implanting pacing electrodes. A guided tissue penetrating catheter is inserted into a blood vessel and a penetrator is advanced from the catheter to a target location. A pacing electrode may be delivered through a lumen in the penetrator.
U.S. Pat. No. 7,881,810 discloses how a heart chamber may be accessed via the pericardial space of the heart. The pericardial space is accessed via a transmyocardial approach or a subxiphoid approach. A lead may, thus, be routed into the pericardial space, through myocardial tissue and into the heart chamber.
US2010/0280565 relates to a catheter-based system for implantation of pacing leads or intramural myocardial reinforcement devices within the myocardial wall of the heart to provide improved cardiac function.